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What Are the Long-Term Effects of Marijuana Use?

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Updated April 18, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Question: What Are the Long-Term Effects of Marijuana Use?
Answer: If you smoke marijuana for a number of years, you can experience some negative consequences, contrary to popular belief among many teens. As the marijuana legalization movement continues to gain momentum in the United States, fewer and fewer teens each year report that they think smoking weed is harmful.

But, National Institute on Drug Abuse research shows that chronic marijuana smoking can negatively affect the brain, the lungs, and for a percentage of users, cause addiction.

What Does Marijuana Do to the Brain?

Numerous studies have found a link between smoking weed and problems with regions in the brain that control learning and memory, appetite, coordination, and pleasure.

One 2014 study found that, compared to non-smokers, even casual use of marijuana can change the size, shape and density of two regions of the brain that are involved in emotion, motivation and decision making.

However, for the most part, the extent of the how long-term marijuana affects the brain is unknown, because most subjects who participate in studies of long-time marijuana smokers also drink alcohol, which has its own negative effects on the brain.

How Does Smoking Marijuana Affect the Lungs?

Research shows that if you smoke marijuana regularly, you can develop many of the same breathing and lung problems that tobacco smokers develop. These include chronic cough and a greater risk of developing lung infections like pneumonia.

There have been no studies directly linking marijuana smoking to developing lung cancer, but marijuana smoke does contain many of the same toxic chemicals, and more, as cigarette smoke. Furthermore, one reason that smoking weed hasn't been linked directly to cancer is because many marijuana users who do develop lung cancer are also cigarette smokers.

Addiction

Most teens believe you simply can't become addicted to marijuana, but NIDA research indicates that is incorrect. About 9% of people who smoke weed end up becoming dependent on it. For those who begin smoking marijuana at an early age, about 16% become dependent.

Of those who smoke marijuana on a daily basis, 25% to 50% meet the diagnosis criteria for marijuana dependency, meaning that they continue to smoke in spite of negative consequences, they experience withdrawal symptoms when they quit, and they experience cravings for the drug if they try to abstain.

Think you don't have withdrawal symptoms when you stop smoking marijuana? Take the Marijuana Withdrawal Symptoms Quiz to find out.

Has smoking marijuana become a problem for you?
Take the Marijuana Screening Quiz

Back to: Marijuana FAQ for Teens

Sources:

Gillman, JM, et al. "Cannabis Use Is Quantitatively Associated with Nucleus Accumbens and Amygdala Abnormalities in Young Adult Recreational Users." The Journal of Neuroscience 16 April 2014.

National Institute on Drug Abuse. "Marijuana." DrugFacts Updated January 2014

National Institute on Drug Abuse. "Want to Know More?- Some FAQs about Marijuana." Marijuana: Facts for Teens Updated October 2013

National Institute on Drug Abuse. "Marijuana." Research Report Series Updated July 2012

The Partnership at DrugFree.org. "Marijuana." Drug Guide. Accessed April 2014.

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